A utility provider, such as a gas, electricity, or water provider, may have a large number of control, measuring, and sensing devices installed in the field in order to control transmission and distribution of the product, measure, and record product usage, and detect problems. Such devices may include water, gas, or electrical meters, remotely controlled valves, flow sensors, leak detection devices, and the like. Utility meters may include wireless communication capability to send and receive wireless communications with a remote communication device, enabling remote reading of meters.
Advanced Metering Infrastructure (AMI), Automatic Meter Reading (AMR), and Advanced Metering Management (AMM) are systems that measure, collect, and analyze utility data using advanced metering devices such as water meters, gas meters, and electricity meters. The advanced metering devices combine internal data measurements with continuously available remote communications, enabling the metering devices to transmit and receive data through the AMI, AMR, and/or AMM network.
A typical AMI network may include thousands of devices called “nodes.” A “node” as used herein may refer to either a composite device in a network capable of performing a specific function or a communication module connected to such a device and configured to provide communications for the device. The AMI network also includes a device known as a repeater, which receives a signal from a central network device, such as a hub, and that regenerates the signal for distribution to other network devices. Nodes and some repeaters are powered by batteries (DC power), while other repeaters are AC powered. Because of the remote placement nature of the nodes and associated devices, it is desirable to maximize a battery life of the nodes and associated devices in order to reduce down time and to reduce the amount of maintenance that must be performed on the nodes. While the battery powering a repeater is frequently more powerful than that of a node, maximizing battery life in a DC repeater is likewise desirable.
One way to maximize battery life of a node and of a repeater powered by direct current (DC) is to only intermittently “listen” for a hailing communication from another network device, whereby the receiving device may only be powered on (i.e., “awake”) for around three milliseconds (ms) to detect whether any hail messages are being sent over alternating hailing channels, and if not, to power off (i.e., “sleep”) for a predesignated time, such as three seconds. This waking-sleeping sequence alternately repeats, with the waking moments called “sniffs” and the interval between sniffs (in this example, the three seconds) known as a “sniffing window.” The receiving device has a channel activity detector (CAD) which, during a sniff, can quickly (in 2-3 ms) assess whether any RF energy exists in the alternating channels that matches a preamble transmission profile. A preamble represents a sequence of symbols that may be repeated at the start of a data message, including a hailing message. The preamble portion of a hail message may have a duration of 160 ms, and the data portion of the message may have a duration of 20 ms. Each hail message is followed by a period of about 22 ms where the hailing device waits to receive the start of an acknowledgement (ACK) signal from the receiving device. If the start of the ACK signal is detected during the 22 ms period, then the hailing device waits to receive the entire ACK signal (which may be longer than 22 ms). Otherwise, without such detection, the hailing device either sends another hail or goes to sleep, depending on whether any predetermined limit on hailing attempts has been reached. During the sniffing window, the hail message is repeated over two or more alternating hail channels. Advantageously, if a sniff does not result in preamble detection of a hail message being transmitted due to the sniff not occurring during transmission of a valid segment of the preamble portion, the next sniff will align with a valid segment of the preamble portion of a later-occurring repeated hail message.
When attempting to hail a node given the above time parameters, if a preamble is not detected by the very first sniff occurring during transmission of a pattern of repeated hail messages, then the hail message will repeat almost 14 times during the three-second sniffing window before the next sniff achieves preamble detection. Additionally, during each hail message, the transmitting device is in a transmission mode approximately 89% of the time (i.e., 1−(22/202)=1−0.1089≈0.89). Thus, although listening only once every 3 seconds is an effective way to save power of the listening device, more burden is placed on the hailing device, which has to use more energy to try to successfully hail the receiving device.
A battery by itself cannot supply sufficient current to power communications between a hailing device and a receiving device; it can output only a small amount of energy for long periods of time. However, when a battery is coupled to a companion device, such as a particular type of capacitor charged by the battery, an AMI device can output sufficient energy for communicating, though for a comparatively shorter period of time. The companion device used for powering communications according to the parameters described above was a Hybrid Layered Capacitor (HLC), which can supply energy for a long time, at a minimum, for the 3-second sniffing window described above. However, HLCs employ proprietary technology and are expensive. Additionally, finding an adequate supply of HLCs has proven difficult.
To overcome these problems, an Electrolytic Double Layer Capacitor (EDLC), also known in the trade as a “super capacitor,” can be used instead of an HLC. Like an HLC, an EDLC can output a sufficient amount of energy to support communications. However, the period of time during which the EDLC can sustain that energy output is much shorter than that for the HLC, specifically, only about 1.5 seconds, as compared with the minimum 3 seconds for the HLC (i.e., entire sniffing window duration). Furthermore, although large EDLCs can supply greater energy than smaller ones, large EDLCs are more susceptible to leakage current, which reduces overall battery life. Hailing a listening device in the manner described above with an EDLC is therefore not feasible. Thus it has become necessary to derive a means of successfully hailing a listening device in an AMI network, such as a DC repeater, that overcomes the foregoing drawbacks.